The number of drivers involved in fatal crashes in Colorado who tested positive for marijuana has risen sharply each year since 2013, more than doubling in that time, federal and state data show. A Denver Post analysis of the data and coroner reports provides the most comprehensive look yet into whether roads in the state have become more dangerous since the drug’s legalization.

Marijuana and DUI fatal crashes by time of day are startlingly different. Marijuana fatal crashes dominates daytime populated rush hour traffic - before and after standard work hours. For 11 consecutive daytime one-hour time periods, 6am to 5pm, the percentage of marijuana crash fatalities exceeded DUI crash fatalities. DUI crashes dominate the evening hours and occur during some of the least populated road times. For 8 consecutive evening time periods, 8pm to 4am, the percentage of DUI crashes exceeded marijuana crashes.